1. Field of the Invention:
The present invention relates, in general, to the field of heating, ventilating and air conditioning systems and, more specifically, to a variable air volume distribution system.
2. Information Disclosure Statement:
It is common in heating, ventilating and air conditioning systems for commercial buildings and the like to vary the volume of air being forced into the conditioned space of the building rather than varying the temperature of the air. A major problem with such variable air volume systems is the need to exhaust substantially the same amount of air from the conditioned space as is being forced into the conditioned space to prevent the air pressure within the conditioned space from increasing or decreasing. One prior art method used with relative small buildings and the like is to merely install automatic relief vents in the building between the conditioned space and the outside atmosphere which will open when the air pressure within the conditioned space goes above a predetermined amount to allow the free passage of air between the conditioned space and the outside atmosphere. However, such a relative passive method is not satisfactory for relatively large buildings.
The inventor is aware of Smith, U.S. Pat. No. 4,437,608 which discloses a variable air volume building ventilation system in which the flow rate within the outside air duct is maintained substantially constant and may be set to substantially match the amount of air which will be normally exhausted from the building by exhaust fans and leakage such that the flow of air in and out of the building is balanced. Because of the relevancy of the Smith U.S. Pat. No. 4,437,608 patent to the present invention, the patents cited in the prosecution of the Smith U.S. Pat. No. 4,437,608 patent are listed below and may be relevant to the present invention: Jauss, U.S. Pat. No. 3,887,127 discloses an electrical control circuit for a ventilation system which is free of any switching device for changing from winter operation to summer operation; Lorenz, U.S. Pat. No. 3,611,906 discloses a ventilating system including dampers in the air inlet for a relatively closed building that are adjustably positioned by a reversible electric motor controlled so that although the velocity at which air is exhausted from the building may vary, the dampers regulate the inflow of air to provide a sustantially constant pressure differential between the interior and exterior of the building; Modes, U.S. Pat. No. 4,073,433, discloses a control apparatus to override the primary pneumatic circuitry of an air distribution system during warm-up cycles; Skinner, U.S. Pat. No. 4,145,161 discloses a speed control for the electric motor of an oilwell beam pumping unit; Knauth, U.S. Pat. No. 4,174,065 discloses a fluid flow regulating system for controlling the motor speed of fluid pumping devices; Robinson, U.S. Pat. No. 4,189,094 discloses a control system which automatically varies the degree of ventilation of an indoor swimming pool in response to variations in the outside temperature; Stewart et al, U.S. Pat. No. 4,191,511 discloses a control for the main gas stream from a compressor which automatically adjusts the amount of gas vented from the compressor output by a variable relief valve or other flow restriction means; Dehart, U.S. Pat. No. 4,251,027, discloses a variable volume control assembly for conditioned air systems and that operates with pressure independent control; Rowe, U.S. Pat. No. 4,284,943 discloses a control apparatus for maintaining a measured parameter of an environment in a closed-loop system within a range of the desired level for that parameter to an accuracy greater than that of the parameter measuring device in the closed-loop system; Haines et al, U.S. Pat. No. 4,407,185 discloses a variable air volume system in which the inflow of outside air is maintained above a predetermined value by maintaining a substantially fixed negative pressure in the plenum by the use of a static pressure sensor and control system for controlling the speed of the return fan.
None of the above methods or patents disclose or suggest the improved variable air volume air distribution system of the present invention including an air supply plenum, a supply fan for transferring air from the air supply plenum into the interior of a building, a return air plenum for receiving air from the conditioned space of the building, and an exhaust fan for exhausting air from the return air plenum to the outside atmosphere; the improvement including a first pressure sensor located in the air supply plenum for sensing the air pressure within the air supply plenum; a second pressure sensor located in the return air plenum for sensing the air pressure within the return air plenum; and control means for causing the exhaust fan to exhaust air from the return air plenum at a rate proportional to the ratio of the air pressures within the air supply plenum and the return air plenum.